This invention relates to the manufacture of mono-crystalline webs of semiconductor material and, more particularly, to a method of manufacture of monocrystalline webs of silicon.
One of the most common methods for pulling single crystal semiconductor material is the Czochralski method wherein a monocrystalline rod is pulled from a melt of the semiconductor material. The monocrystalline rod must then be sawed, lapped and polished into suitable wafers for the production of semiconductor devices. Another method of producing monocrystalline semiconductor material is a "float zone" technique, wherein a monocrystalline rod is pulled from a melt within, or on top of, an ingot of polycrystalline material. Again, this technique produces a monocrystalline rod which must be sawed, lapped and polished to produce wafers suitable for semiconductor production.
It has previously been recognized that large savings of material could be made if the monocrystalline semiconductor material could be produced directly in ribbons or strips that approximated at least one dimension of the semiconductor device to be processed. However, problems with control of the molten region, the thermal profile, both vertical and horizontal, and growth rate, have prevented various suggested ways of doing this from attaining commercial acceptability.
With the present need for new energy sources, many suggestions have revolved around the use of solar energy. One way solar energy can be utilized is with solar cells, whereby the radiant solar energy is converted directly to electrical energy. Systems using solar cells will require large amounts of semiconductor material, particularly silicon, if such systems are to become acceptable. Such silicon must be attainable at a cost far less than present costs for transistors, rectifiers, etc.